Condensed Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Collaboration revenues:
License and milestone revenue		$ 1,143		$ 3,429
Total collaboration revenues		1,143		3,429
Grant revenues		521	147	732
Total revenues		1,664	147	4,161
Operating expenses:
Research and development	11,743	10,751	35,061	30,605
General and administrative	2,796	3,131	8,324	8,749
Total operating expenses	14,539	13,882	43,385	39,354
Loss from operations	(14,539)	(12,218)	(43,238)	(35,193)
Interest expense, net	(457)	(516)	(1,429)	(1,444)
Net loss	$ (14,996)	$ (12,734)	$ (44,667)	$ (36,637)
Net loss per common share:
Basic and diluted net loss per common share (in dollars per share)	$ (0.25)	$ (0.26)	$ (0.77)	$ (0.79)
Basic and diluted weighted average number of common shares outstanding (in shares)	60,661,720	49,403,589	58,235,263	46,446,328